In 2017, Jonathan starred as Edgar alongside Sir Ian McKellen in a production of King Lear at the Chichester Festival Theatre, and his role required him to show a lot of skin. "Basically, I had to run about in a thong in the rain. [Ian] would get soaked as well, so afterwards we'd warm up, have a cup of tea and a chat," he told Attitude in October 2018. Luckily, it ended up being a bonding experience. "He was everything you could wish for and more, so brilliant," he added in reference to Ian. "After rehearsals, we'd order Deliveroo, sit on the picnic benches and put the world to right. He used to tell me, 'Just live your life', and he is very much someone who has."
Later, when he was interviewed by Ian for Attitude in December 2020, Jonathan jokingly reminded the actor how they first met. "We met on day one of rehearsals of King Lear, in which we were both going to appear nude on stage," he said.