The answer is YES.
Ethereum is a fork of Ethereum Classic, and is much more valuable than the original.
There is no law saying the original coin must be the most valuable -that is decided by the market. In the case of Ethereum, Vitalek Buterin backed the forked coin and market money flowed to it.
ETH is indeed a fork of Ethereum, however the thing that did not fork is the majority of the community. That chose to step across and treat it as something essentially unchanged. Ultimately it's the community that imparts the value and decides how legitimate something is.
Other than that, Lisk was forked from something named Crypti but I'm not sure whether Crypti was ever a fully live chain. There are probably more than a few others too in these rebooting times.