Mick Jagger has taken to Instagram after it was revealed that Gabriel, his youngest son with ex Jerry Hall, married earlier this month.MORE: Mick Jagger, 77, appears in very rare photo with his four-year-old sonSharing a picture on his 78th birthday, the Rolling Stones star thanked his two million followers for the well wishes and revealed how he had spent the day. WATCH: Mick Jagger thanks fans for the birthday wishes"Thanks so much for all your birthday wishes," he captioned the post, which