Was Anne of Cleves ugly?

No, there is no evidence to back that up. Here is an extract from an article I wrote on this (see https://www.theanneboleynfiles.com/8390/anne-of-cleves-flanders-mare/):

Although Anne of Cleves has gone down in history as the Flanders Mare, the wife who was ugly and looked like a horse, it is only Henry VIII who seems to have considered her ugly. In January 1539, Henry VIII sent Christopher Mont, a member of Thomas Cromwell’s household, as ambassador to Germany to discuss a possible marriage between the Princess Mary and William, Anne of Cleves’ brother, and to “inquere of the beautie and qualities of the lady eldest of booth doughters to the duke of Cleves, as well what stature, proportion and complexion she is of as of her lerning actyvitie, bihauiour and honest qualities”. Mont reported back that “everyone praises the lady’s beauty, both of face and body. One said that she excelled the Duchess [of Milan] as the golden sun did the silver moon”, although he was going on hearsay as he had not seen Anne himself.

In March 1539, Henry sent ambassadors to Cleves to get further reports on Anne and to get a portrait of Anne but the ambassadors encountered difficulties as Anne and her sister kept their faces covered. In the summer of 1539, Henry sent his court painter, Hans Holbein, to Cleves to paint Anne and her younger sister. When the leading English ambassador, Nicholas Wotton, saw Holbein’s portraits of the sisters, he declared that the artist “hathe expressyd theyr imaiges verye lyvelye” and that others also considered the portraits a good likeness of the young women. Although we do not know what Henry thought of Anne from her portrait, we have to conclude that he liked what he saw as he continued with negotiations. Why then did the King take an instant dislike to his bride-to-be when he first encountered her at Rochester on New Year’s Day 1540? Why did he adamantly declare “I like her not”?

In my opinion, Henry was humiliated and embarrassed by their first meeting, which had been a complete disaster. Always the romantic, Henry had decided to surprise Anne by disguising himself in the great chivalric tradition and intercepting her on her way to London. According to this tradition, the would-be bride would see through the disguise, fall in love at first sight and swoon into her beloved’s arms, it would be the perfect first date and they would both live happily ever after. Unfortunately, Anne knew nothing of this tradition, did not recognise Henry and was shocked and scared by this monstrous man who tried to embrace her and take such liberties with her. She acted in an entirely proper way but she failed to recognise Henry for who he was and failed to react in the way that Henry had anticipated. We don’t know whether Anne lived up to her portrait, but I think it was her reaction to Henry which sealed her fate. If she had been ugly then why did nobody else notice and why did Holbein risk painting her the way he did? Of course, it could be that Anne with her tall stature, her rather long nose and heavy lidded eyes was just very different to Henry’s previous wives, perhaps she just wasn’t Henry’s type?